This application is related to U.S. patent application Ser. No. 09/124,200 filed by John J. Janssen et al. on even date herewith and entitled xe2x80x9cTransient-Suppressing Mode Switch.xe2x80x9d The related application is assigned to the assignee of the present application and hereby incorporated herein in its entirety by this reference thereto.
This invention relates generally to pulse shaping of digital data, and more particularly to using look-up tables to accomplish pulse-shaping.
In wireless communications systems, pulse-shaping of digital data is usually needed to meet system spectral emission requirements. Instead of using conventional filters to shape pulses, however, a look-up table is often used to approximate the filtering operation and reduce the cost and complexity of the pulse-shaping operation. The digital data is translated into digital words, and a look-up table maps each digital word to an output waveform segment stored in the table. Due to the look-up table, the first output waveform segment in a pulse-shaping digital data output waveform sequence may have an abrupt transition from a zero value to a positive or negative value. Likewise, the last output waveform segment in an output waveform sequence may have an abrupt transition from a positive or negative value to a zero value. These turn-on and turn-off transients may cause unacceptable spectral emissions.
Thus, there is a need for a pulse-shaping look-up table that reduces the turn-off and turn-on transients caused by traditional pulse-shaping look-up tables.